The present invention relates to print substrate handling and duplex reproduction and more particularly to a short edge feed duplex operation producing book style duplex prints.
In an electrostatographic reproducing apparatus commonly in use today, a photoconductive insulating member is typically charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image areas contained within the usual document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with developing powder referred to in the art as toner. Most development systems employ a developer material which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development the toner particles are attracted from the carrier particles by the charge pattern of the image areas in the photoconductive insulating area to form a powder image on the photoconductive area. This image may subsequently be transferred to a support surface such as copy paper to which it may be permanently affixed by heating or by the application of pressure. Following transfer of the toner image to a support surface, the photoconductive insulating member is cleaned of any residual toner that may remain thereon in preparation for the next imaging cycle.
Duplex copying, i.e. copying image information to both sides of a single sheet of paper, is an important feature in copying machines. Duplex copying is desirable because it reduces the amount of paper required in copying in comparison to simplex (single side) copying, produces attractive copy sets, and can simulate the appearance of a printed book. Generally, such copying is accomplished in either one of two methods. In a first method, first side copies are produced in a reproduction processor and stacked in a duplex tray. When a set of first side copies is complete, the copies are fed out of the duplex tray and returned to the reproduction processor with an odd number of inversions in the total duplex path to receive second side image information, and subsequently passed to an output. Alternatively, first side copies may each be returned directly to the reproduction processor to receive second side copies thereon, without stacking, for example, as described in U.S. Pat. No. 4,660,963). This type of copying finds particular use with respect to copying two documents placed on a platen for sequential copying, sometimes referred to as two-up copying.
Book style duplex copying, as used herein refers to the production of duplex copy sets which are suitable for reading as a book from top to bottom from the same sheet edge, with the image top portion on both sides of the sheet adjacent the top edge of the sheet, for binding along a side edge with respect to the image. This portrait style image appearance is generally only achieved in the present duplex-capable reproduction machines, however, when copy sheets are fed through the reproduction processor to receive image information on one or both sides of the copy sheet with the image top to bottom alignment or orientation, as the image is normally viewed, oriented on the sheet transverse to the direction of sheet feeding. When duplex copies are made with image top to bottom alignment oriented on the sheet in the direction of sheet travel in the same reproduction machines, the resulting two-sided copies do not have the top portions of the image along a common edge of the sheet. Instead, the image top portions are adjacent opposed edges on each side of the sheet, which, when the copy set is bound along a side edge in a book style format, provides the second sides of the sheets upside down with respect to the first sides of the sheets. This type of copying is sometimes called military style duplex, and hereinafter referred to as pad style duplex, provides easy viewing only if the copy set is bound along the top edge and read by turning pages upwardly to read the back side of each sheet. While pad style duplex copying has certain applications, it is frequently undesirable in duplex copying usage.
Heretofore, in duplex capable copying machines where it has been desirable to provide book style duplex copying from simplex originals, it has been necessary for the machine to provide a paper path and processor accommodating LEF (long edge first) sheets and place images on the sheet having a top to bottom alignment oriented transverse to the direction of sheet travel. This arrangement adds significantly to the cost of the machine, as it requires the paper path and processing elements to accommodate the long edge of sheets fed through the machine. In very low cost machines it is desirable to provide only a narrow processor, accommodating for example, 81/2.times.11 inch sheets fed SEF (short edge first). The width of the paper path and processing elements in such a machine are only required to accommodate the 81/2 inch length of the sheet as opposed to a machine required to accommodate at least 11 inch widths to accommodate the long edge feed of 81/2.times.11 inch sheets. However, this narrow process width arrangement ordinarily precludes the desirable book style duplex from simplex documents, as the bulk of simplex documents copied have images oriented with the image top portion adjacent a short edge of the document sheet. Alternatively, an operator desiring to produce duplex copies from simplex documents on SEF sheets, must manually rotate every other document to be copied by 180.degree. prior to copying. This is inconvenient, and potentially confusing, allowing the possibility of operator errors. Additionally, such an arrangement precludes the simple use of automatic document feeders to feed the set of documents to be copied past the platen, as an operator seeking to take advantage of the increased speed in automatic document handling must manually prepare the set of simplex documents to be copied with every other sheet rotated with respect to the previous sheet, and re-order the document set subsequently to copying.